Question

Consider an ionic compound, MX, composed of generic metal M and generic, gaseous halogen X. The enthalpy of formation of MXis ΔH∘f=−427kJ/mol. The enthalpy of sublimation of Mis ΔHsub=135kJ/mol. The ionization energy of Mis IE=433kJ/mol. The electron affinity of Xis ΔHEA=−307kJ/mol. (Refer to the hint). The bond energy of X2is BE=175kJ/mol. Determine the lattice energy of MX.

Answer 1

Answer:

The lattice energy of MX is -523.5 kJ/mol.

Explanation:

$M(s)+\frac{1}{2}X_2(g)\rightarrow MX(s),\Delta H_f=-427kJ/mol$....[1]

$M(s)\rightarrow M(g),\Delta H_{sub}=135kJ/mol$....[2]

$M(g)\rightarrow M^+(g)+1e^-,I.E=433kJ/mol$....[3]

$X(g)+e^-\rightarrow X^-(g),E.A=-307kJ/mol$....[4]

$X_2(g)\rightarrow 2X(g), \Delta H_{X-X}=175kJ/mol$....[5]

$M^+(g)+X^-(g)\rightarrow MX(s),L.E=?$....[6]

[1] = [2] + (1/2)[5] + [6] - [3] - [4]

$-427kJ/mol = 135kJ/mol +\frac{1}{2}\times 175kJ/mol+L.E- (433kJ/mol) - (-307kJ/mol)$

$-427kJ/mol=96.5 kJ/mol+L.E$

$L.E=-523.5 kJ/mol$

The lattice energy of MX is -523.5 kJ/mol.